The present invention relates to a three-speed speed changing mechanism that includes two planetary gear sets and a movable gear is controlled to be engaged with one or the two or both of the two planetary gear sets so as to obtain three different speeds.
A conventional electric tools, especially for those tools have a rotating output shaft such as electric drills, are equipped with a speed reduction mechanism so as to provide different speeds and torque. In general, the speed reduction mechanism uses a planetary gear set and an input shaft is engaged with a chosen gear such as the sun gear, the inner gear, or the planet gears so that different speeds can be obtained. Nevertheless, due to the limited space in the casing of the tools, only two speeds can be obtained by the mechanism, and the speeds and torque are not satisfied by the users.
The present invention intends to provide a speed changing mechanism that outputs three different speeds by movably engaging a movable gear between two planetary gear sets.
In accordance with one aspect of the present invention, there is provided a speed changing mechanism which comprises a base in which a first planetary gear set and a second planetary gear set are respectively received. An input device and an output device are also received in the base. A movable gear is received in the base and has bosses which are movably engaged with protrusions in the base and a ring member of the input device. The planet gears of the two planetary gear sets are respectively engaged with the input gear of the input device. The movable gear is movably engaged between the two planetary gear sets. A push button controls the movable gear so as to engage the desired gears to output two different speed. When the movable gear is positioned in dependent from the two planetary gear sets, a third speed can be obtained.